1. Technical Field
The invention relates to sampling apparatus and in particular to a sampling apparatus for withdrawing a sample of non-free flowing granular material moving through a pipe. More particularly, the invention relates to such a sampling apparatus which withdraws samples of non-free flowing granular material moving through a pipe at a selected point along the pipe and at selected intervals, and which deposits the samples into a suitable receptacle.
2. Background Information
Various types of samplers have been used to withdraw samples of granular material or slurries from pipes or ducts. In many of these sampling apparatus, the material flows into an opening in a probe and is subsequently removed usually in one of three ways. Either the material pressure in the pipe forces the sample out of the probe, gravity causes the sample to move through and out of the probe, or a fixed increment of material is collected in a cavity at the end of the probe and is dumped into a chute such as by rotation of the cavity member. Such samplers depend on the flowability of the material into and/or out of the probe. Some examples of such prior art samplers are shown in U.S. Pat. Ser. Nos. 1,966,712, 2,370,260, 3,659,461, 3,747,411, and 4,433,587. However, several of the samplers shown and described in the above-listed patents are unsuitable for obtaining representative samples of non-free flowing materials, such as crushed coal or materials that have a tendency to plug up the probe opening. Also, many of these prior art sampling apparatus do not sample across the entire width of the pipe. Finally, all of these prior art samplers utilize a round tube which draws disproportionately larger amounts of sample material at the axis of the probe than the sides. This creates undesirable sample bias in a highly heterogeneous material such as coal.
Other types of known samplers utilize an auger to withdraw material out of a pipe. One example of such a sampler is the Model B Automatic Sampling System manufactured by Gustafson of Plano, Tex. While such samplers only require material to flow into the auger, the auger constantly remains in the pipe and creates a source of blockage for non-free flowing materials, especially when the material is wet. In addition, such routinely present protrusions are not permitted in coal pipes. Although retractable augers are utilized to extract coal samples vertically from truck and rail car beds, there is no known retractable auger adapted for use in pipes. Finally, these prior art auger-type samplers all utilize a round probe tube which, as discussed above when mounted on a pipe perpendicular to the movement of material within the pipe, takes disproportionately more sample at the axis of the probe than its sides.
A different principle has been applied in the known prior art to the sampling of coal from trucks and rail cars, in which both static and vibratory forces are applied vertically to a rectangular probe having a rigid cutting edge providing for filling of the probe with a core of the material to be sampled. Such a construction is shown and described in U.S. Pat. Ser. No. 3,158,030. In the sampler of this prior art patent, a pair of pneumatic closing gates hold the core sample in the probe following penetration of the material by the probe. The probe then is vertically withdrawn, moved horizontally to the location of discharge, and the gates opened to release the sample into a receptacle or onto a belt. This device does have the potential advantage of removing a long, uniform cross-section sample of a non-free flowing material. Also, the pneumatic vibrations greatly assist the penetration of the coal by the sampler probe and movement of material into the probe. However, although the general principle of static and vibratory penetration by a rectangular tube having a rigid cutting edge into a material is applicable in the present invention, known prior art samplers which utilize the vibratory theory require complete removal of the probe from the material being sampled and movement to another location for discharge of the sample, and the sample is discharged out of the same opening through which the sample entered the probe. In addition, there is no provision either to seal the vibrating rectangular probe into a pipe or to isolate such a pipe following removal of the probe.
It is known that the forces needed to move a solid material through a straight tube of narrow cross-section increase with the distance from the point of entry into the tube due to the increasing friction of cumulative layers of the material. Even with the assistance of vibratory forces, under certain conditions movement of such material into a straight three inch by three inch square probe, for example, rapidly becomes more difficult as the tube fills up. The rate of movement of material into the probe is critical for sampling from a non-free flowing material moving in a pipe, since as the length of time the probe remains inserted in the pipe increases, the chance of initiating blockages in the pipe also increases. This is especially critical where the material to be sampled has a high moisture content.
Thus, the need exists for an improved sampler for non-free flowing granular material moving through a pipe in which representative samples of the material can be quickly and efficiently removed from the pipe at a selected point along the pipe and at selected intervals without significantly blocking the pipe, and then deposited in a suitable receptacle for subsequent analysis.